This invention relates generally to the field of telecommunications, particularly to digital switching systems used to route calls within telecommunication networks, and more particularly to a method for bypassing the common control and switch matrix of a digital switching system.
A class 5 central office comprises a building or room which houses a class 5 switching system, which operates to connect telephones and other devices used by end-user customers (xe2x80x9csubscribersxe2x80x9d) to a telecommunications network such as the public switched telephone network (xe2x80x9cPSTNxe2x80x9d). A class 5 digital switch also converts the analog signals used by telephones, modems, FAX machines, and some PBX trunks, into the digital signals that are routed through a digital telecommunications network. The class 5 digital switch also provides special services for caller ID displays and message waiting lights for subscribers, and it processes and routes calls from digital PBX trunks, ISDN lines, and digital loop carriers (xe2x80x9cDLCxe2x80x9d) to a telecommunications network.
The class 5 central office houses substantial amounts of both equipment and cabling that is designed for a service life measured in decades, because it is extremely difficult and expensive to undertake replacement. To illustrate the physical magnitude of the equipment and cabling, consider that for each telephone line connected directly to the class 5 switch, a pair of copper wires is routed from a subscriber""s premises to the class 5 central office. Large installations have hundreds of thousands of such pairs of wires that must be organized, physically supported, and accessible for maintenance. Cables with hundreds of such pairs of wire typically enter the class 5 central office through an underground cable vault. The individual pairs of wire leave the cables and run along a main distribution frame (xe2x80x9cMDFxe2x80x9d), which provides connection points for test access and connecting to the switching system. The MDF in a large office may be hundreds of feet long to provide many thousands of necessary connection points. Other cables are routed from the connection points of the MDF to line/trunk frames in the class 5 digital switch, which contain the electronics to terminate each telephone line, convert analog signals to digital signals, monitor each line for on-hook and off-hook conditions, dialing, etc. In a similar fashion, other cables are routed from the line/trunk frames, through the MDF or other distribution frame, out of the class 5 office and to the interexchange and long distance networks, where calls are carried from one class 5 switch to another. There may a hundred or more line/trunk frames in a large office, representing an investment of millions of dollars.
Most of the physical plant of the class 5 central office consists of wire, distribution frames, and line/trunk frames. A much smaller portion of the physical plant is devoted to a switch matrix and a common control system. The switch matrix routes calls from one line to another line or trunk, depending on whether the call is to a number in the same central office or a different central office. The common control comprises, among other things, a stored program control system (xe2x80x9cSPCSxe2x80x9d), which performs call processing, manages the hardware and software of the switch matrix and the line/trunk frames, and manages various communications interfaces to external software systems such as for billing, surveillance, maintenance, and provisioning.
As mentioned previously, the class 5 switching system and its associated cable plant are physically large, expensive, and engineered to remain in service for decades. As mentioned before, replacing such a switching systems is extremely difficult and cost-prohibitive. For these reasons, most subscribers are connected to switching systems that were originally designed years ago, before the deregulation of telecommunications that has taken place around the world. Therefore, they are referred to as xe2x80x9clegacyxe2x80x9d switching systems.
The deregulation of telecommunications and the rise of the internet have engendered a number of important trends. One trend is the mergers and acquisitions between telephone companies, which leads to the problem of consolidating different networks. While the trunks that carry digital voice and data are inherently compatible with industry standards, consolidating the disparate billing, provisioning, and maintenance software systems that communicate with the SPCS of each class 5 digital switch has proven difficult and expensive. Furthermore, the hardware and software of switching systems are proprietary to each particular manufacturer; therefore, the presence of more than one vendor""s switching equipment make it difficult to eliminate redundant costs in the consolidated network. For example, periodic software updates must be purchased for the SPCS of each brand of switching system in the consolidated carrier""s network.
Another trend is competition. Competing telephone services, offered by cable television operators, electric utilities, and other competitive providers, often use switching equipment of much newer design that enables the competitive provider to more easily create diverse service packages to offer to customers of traditional telephone companies. The class 5 digital switches owned by incumbent telephone companies were designed for the era of the monopoly telephone company. Consequently, their stored program control systems are not very flexible. The incumbent telephone company is therefore not able to easily create new service packages, but must often wait for years for new features to be added to proprietary software by the manufacturer of the legacy class 5 switching system.
Another trend is toward networks that carry both voice calls and data over common transport based on connectionless access protocols such as asynchronous transfer mode (xe2x80x9cATMxe2x80x9d) and transport control protocol/internet protocol (xe2x80x9cTCP/IPxe2x80x9d), also referred to as xe2x80x9cpacket networksxe2x80x9d. Packet networks simplify the problem of carrying voice and data from region to region. Furthermore, routing calls over such a network permits the use of common routing hardware controlled by so-called xe2x80x9csoft switchesxe2x80x9d, which are not much more than computers running specialized software. xe2x80x9cMedia gatewaysxe2x80x9dare packet switches that also convert the digital format of voice calls on trunks from legacy class 5 switches into the formats used in packet networks. However, merging traditional class 5 digital switches into a converged network poses problems similar to those of merging networks of different equipment, such as different maintenance, provisioning, and billing software systems. Furthermore, external software systems are necessary to convert the protocols used for setting up calls across ATM and TCP/IP networks back to the corresponding protocol used by the stored program control systems of legacy class 5 switches. Moreover, subscribers are still connected through the legacy class 5 switch, and therefore the services and features available are limited to what is available in the SPCS of the legacy switch.
Another trend is the growth of modem calls, mainly for internet access. Legacy class 5 digital switches were designed for an average call duration of approximately three minutes. The capacities of the switch matrix and the interexchange trunks were engineered by this standard. In other words, the switch matrix and the interexchange trunks can handle simultaneous calls to or from a certain fraction of the attached lines, that fraction having first been determined before the internet. With large numbers of internet modem calls that average 30 minutes or longer, these capacities are being strained. Expanding the trunk and matrix capacities of a legacy class 5 switch is very expensive.
In addition, the long service life of legacy class 5 digital switches is causing problems of maintenance. As the older legacy equipment ages, it is increasingly difficult to find technicians sufficiently knowledgeable to maintain the legacy equipment, and spare parts are becoming increasingly difficult to find. Third party manufacturers can be found who will supply spare line and trunk modules, which tend to be simpler than other modules and are available second-hand in greater numbers. The much lower volume of common control and switch matrix modules, however, combined with their greater complexity, makes them much less attractive to third party manufacturers. Furthermore, the software that operates in legacy stored program control systems may no longer be supported by its original manufacturer.
It can be seen that most of the limitations of legacy class 5 digital switches are associated with the SPCS and switch matrix, which represent a small part of the physical plant of a central office. On the other hand, the massive physical plant associated with line/trunk frames performs a job that continues to be needed in support of millions of miles of wire that already connects subscribers, through their existing telephones, modems, FAX machines, and PBX""s, with the central office. The problem is that the line/trunk frames are designed to work only with the common control and switch matrix of the same manufacture, thereby preventing another class 5 switch or media gateway from being used to overcome the limitations of the common control and switch matrix.
What is needed is a means to bypass the common control and switch matrix of a legacy class 5 switching system in a way that permits any other switching system or media gateway to perform the associated functions, so that the legacy software may be discarded and/or any limitations of the legacy switch matrix may be overcome, while retaining the legacy line/trunk frames and cable plant and incurring minimal changes to the overall physical plant of the legacy class 5 central office.
A Digital Loop Carrier (xe2x80x9cDLCxe2x80x9d) is an architecture and protocol that defines a means of providing analog and digital lines and trunks at a location remote to the class 5 switching system, using digital transmission facilities from the central office to the remote location, such as high-speed fiber optic facilities. The equipment comprising the remote end of the DLC architecture is called the xe2x80x9cremote terminalxe2x80x9d, while the equipment comprising the end local to the class 5 switching system is called the xe2x80x9clocal terminalxe2x80x9d or the xe2x80x9ccentral office terminalxe2x80x9d. The DLC concept was created to provision telephone service to concentrations of subscribers thousands of feet from a central office, without the expense of running a pair of wires for each end user across the entire distance.
At least two industry standards have been developed that govern digital loop carrier architectures and protocols. In particular, there is the architecture and associated protocol documented by Telcordia Technologies, Inc. (formerly Bellcore) in their document GR-303-CORE (xe2x80x9cGR303xe2x80x9d), which is hereby incorporated by reference. All modern class 5 switches and media gateways are able to operate as local terminals in GR303 DLC""s.
Therefore, what is needed is a method of bypassing the common control and switch matrix of a first class 5 digital switch, by providing a switching system interface which couples one or more line/trunk frames of the first digital switch to one or more digital transmission facilities that make up the remote end of a DLC, where the local terminal is a second class 5 digital switch or media gateway.
What is further needed is to equip such a switching system interface with the means to intercept end user calls dialed to known Internet Service Providers (xe2x80x9cISPsxe2x80x9d) and divert said calls to trunks dedicated to internet traffic.
It is, therefore, an object of the invention to provide such a method and such a switching system interface.
It is a primary object of this invention to provide a method of bypassing the common control and switch matrix of a class 5 digital switch, so that their limitations may be overcome while retaining the large investment in line/trunk frames and cable plant.
It is a further object to provide a means of coupling the line/trunk frames of a first class 5 digital switch to one or more industry standard digital transmission facilities that make up the remote end of an industry standard DLC architecture, so that the line/trunk frames associated with the first digital switch may be operated by a local terminal which may be a second class 5 digital switch or media gateway of any manufacture.
It is a further object of this invention to permit the software operating on the stored program control system of said first class 5 digital switch to be discarded.
It is a further object of this invention to permit most or all of the hardware of the common control and switch matrix associated with said first class 5 digital switch to be decommissioned.
It is a further object of this invention to provide the ability to intercept calls dialed to any one of a list of known ISPs to be intercepted and diverted to trunks dedicated for internet traffic, thus relieving the host switching system or media gateway of a significant portion of internet traffic.
In accordance with the present invention, a method comprises accessing the proprietary signals of a digital switching system that communicate between the line/trunk frames and the common-control-and-switch matrix; providing a switching system interface comprising interfaces compatible with the proprietary signals and also comprising at least one network interface connected to the remote end of a corresponding digital transmission facility of a DLC architecture; and connecting the compatible interfaces to the proprietary signals.
Also in accordance with the present invention, a switching system interface comprises one or more network interfaces for terminating digital transmission facilities; one or more interfaces for coupling to line/trunk frames; a time-slot assignment means for connecting time slots of the digital transmission facilities to those of the line/trunk frames; and a call processing means for coordinating call setup and teardown between the DLC host and the line/trunk frames, and for managing the time-slot assignment means to complete calls.